1. Field of the Invention
The present invention relates to an apparatus and method for independently controlling damping force coefficients of four tire wheel suspension units (shock absorbers) of an automotive vehicle.
2. Description of Background Art
A Japanese Patent Application First Publication No. Showa 61-163011 exemplifies a vehicle suspension control apparatus.
A suspension control apparatus disclosed in the above-identified Japanese Patent Application Publication includes shock absorbers (also called dampers but herein after referred to as shock absorbers) generally located on respective four tire wheels.
In the above-identified Japanese Patent Application, sprung mass (namely, vehicle body) vertical velocities and relative velocities between the sprung mass and an unsprung mass (namely, each of tire wheels and associated tire wheel suspension members) are detected. If both signs (an upward direction is plus and a downward direction is minus) of the sprung mass vertical velocity and relative velocity are mutually the same, the related shock absorber is controlled to provide a hard characteristic for the shock absorber damping characteristic. On the other hand, if both signs described above are mutually different, the related shock absorber is controlled to provide a soft characteristic for the shock absorber damping characteristic.
Such a control method as described above is called suspension (shock absorber) control based on a "sky hook" theory and is carried out independently of the respective shock absorbers on the respective four tire wheels.